It is known, e.g. from Swiss Pat. No. 560,953, to preheat a metal wire above the fusion point of a mass of thermoplastic particles through which heated wire is continuously passed so as to cause adhesion of some of the particles thereto. Upon emerging from that mass, the wire is reheated to fuse these adhering particles into a continuous envelope. It has also been proposed to coat various articles with thermally softenable particulate matter by suspending the comminuted coating material in a fluid, e.g. in a moving gas stream forming a fluidized bed, and exposing the articles to prolonged contact with the material so suspended.
In all these instances the rate of coating is limited by the existence of what may be termed an abrasive threshold, i.e. a velocity beyond which the article to be coated must not move through the mass lest particles already adhering to its surface be again dislodged therefrom by the impact of other, stationary or slow-moving particles colliding therewith. In the specific case here envisaged, i.e. the coating of a metal wire, this abrasive effect is found to increase with the wire velocity.